Radio direction finding means for aviation trainers



Sept. 28, 1948. K. A. KAIL RADIO DIRECTION FINDING MEANS FOR AVIATION TRAINERS Original Filed Jui so, 1945 2 Sheets-Sheet 1 KARLA. KAIL IN V EN TOR.

FIG. I

BY {f ATTORNEYS Sept. 28, 1948. K. A. KAIL RADIO DIRECTION FINDING MEANS FOR AVIATION TRAINERS Original Filed July 30, 1943 2 Sheets-Sheet 2 KARL A. KAI L INVENTOR. FIG. 2

/- 'fl/W ATTORNEYS Patented Sept. 28, 1948 RADIO DIRECTION FINDING MEANS FOR AVIATION TRAINERS Karl A. Kail, Montrose, Pa., assignor to Link Aviation, Inc., Binghamton, N. Y. a corporation of New York Original application July 30, 1943, Serial No. 496,738. Divided and this application June 19, 1944, Serial No. 540,977

2 Claims. (Cl. 35-10) My invention relates to trainers for aviators and comprises means for improving in a grounded aviation trainer means for simulating the functioning of certain of the instruments in such a trainer.

This application is a division of my application Serial Number 496,738, filed July 30, 1943, for Magnetic compass indicating system for aviation trainer, s-ince matured into Patent No. 2,445,673, dated July 20, 1948. I

.It is the principal object of my invention to pro-- vide an improved radio direction finding system for use in a grounded aviation trainer.

The detailed objects of my invention will be understood by the following description and appended claims. In order that the description may be more readily understood reference is made to the accompanying figures wherein Fig. 1 shows a general view of the trainer and instrument system which my present invention comprises.

Fig. 2 is a diagrammatic view of the instrument system of this invention.

Reference is now made to Fig. 1 which shows a trainer of the type disclosed in U. S. Patents 1,825,462 and 2,099,857. These trainers, which are of .the type manufactured by Link Aviation Devices, Inc, of Binghamton, New York, comprise a fuselage lo which is mounted upon a universal joint (not shown) positioned near the central part of the floor of the fuselage. A pair of bellows "l2 known as the elevator bellows are provided and through a system of vacuum, valves and linkages these bellows maybe made to pitch fuselage ii) in simulation of the climbing and diving of'a plane in actual flight. A second pair of bellows, known as the aileron bellows, are used to bank the fuselage l laterally in simulation of the bankin of a plane in actual flight. Only one of these aileron bellows is shown and it is designated I4. Still referring to Fig. 1, it will be seen that a triangular base 16 is provided, and rigidly attached thereto is a lower "bearing housing I8. Formed integrally with the upper end of this bearing housing is an exterior annular groove .20. Inside lower bearing housing [8 and rigidly afiixed thereto is ring gear 22. Base l6, lo'wer housing l8, annular groove 20 and ring gear 22 are fixed in relation to the floor upon which base 16 rests. Upper bearing housing 24 is rotatably mounted with respect to lower housing l8 by means of a suitable bearing arrangement and rigidly attached to housing 24 is platform 26 upon which rests the triangular tower 28 which holds the fuselage l0 and otherassociated apparatus. Bigidly afilxed to and depending from platform 26 is turning motor 30 which has an output shaft upon which is rigidly affixed a wheel 32 which also is grooved. Turning :belt 34, it will be noticed, wraps around groove integral with fixed lower bearing housing I8 as well as around the output wheel 32 of turning motor 30. Whenever the student in the trainer presses one of the rudder pedals (not shown) therein, turning motor is actuated and the output wheel 32 rotates in a direction dependent upon which rudder pedal is pressed. The friction between groove 20 and belt 34 on the one hand, and wheel 32 and belt 34 on the other, is sufficiently great to prevent slipping therebetween, and consequently, wheel 32 travels along belt 34 causing motor 30, platform 26, tower 28., fuselage H1 and upper bearing housing 24 to rotate in simulation of the turning of a plane in actual flight.

Also seen in Fig. 1 is an operator's desk 35 which has placed thereupon a map 36 over which recorder 31 travels. A detailed description of recorder 31 may be found in U. S. Patent 2,179,663, and as there disclosed it moves forward over the r map or chart 36 to simulate the forward travel fore, a more detailed description is omitted, but

for a thorough explanation thereof reference is made to the above-mentioned United States patents.

Radio compasses and radio direction finders are commonly used in present-day aircraft to determine the direction of a radio station with respect to the longitudinal axis of the plane in a manner somewhat similar to the way magnetic compasses are used to determine the direction of the magnetic pole with respect to the longitudinal axis of the plane. There are various types of radio compasses but all types utilize as a fundamental principle the fact that a loop antenna is highly directional and when the loop is in the plane of the waves of the radio transmitting station a maximum voltage is induced in the loop but when the plane of the loop is perpendicular to the path of the waves a minimum voltage is induced therein. Different designs of radio compasses indicate this maximum or minimum by different methods, the two most common being by means of a left-right visual indicator or by a null (no signal in earphones) In actual flight the bearing of the radio station with respect to the longitudinal axis of the plane is accomplished by rotation of the loop antenna until the indicating instrument (visual or aural) gives the desired indication (pointer centered or no signal heard in the earphones), whereupon the bearing is shown by the visual indicator, or in the case of the aural system, by a pointer and azimuth scale, one of which is mechanically connected with the loop antenna and rotates therewith, the other having a fixed position.

The following improved means are provided by my present invention in order that the practice 7 of taking bearings by means of radio in a plane in actual flight may be more exactly simulated in a grounded aviation trainer.

Reference is made to Fig. 2 which shows a unit 40 which generates a source of radio frequency carrier waves modulated by any desired audio frequency source. Transmitter 40 is preferably of the type discsed in the copending application of Gregor L. Lang, Serial Number 440,950, filed April 29, 1942, since matured into Patent No. 2,435,502, and is preferably located in the desk 35. By means of lead 42 the modulated radio frequency waves are carried to transmitting antenna 44 which takes the form of a rotatable coil of wire. This rotor coil 44 is aflixed to a rotatable vertical shaft 46 which has attached to its upper end a movable index knob and pointer 48 which moves across the face of a scale 50 graduated from zero to 360, scale 50 being fixedly mounted upon a part of the housing of the unit. The unit is in drawer 52 of desk 35. Rotor coil 44 is positioned within a pair of perpendicularly disposed coils 54 and 56. Rotor coil 44 and coils 54 and 56 form what is commonly referred to as a g-oniometer, and they are designated by 58 in Figs. 1 and 2. A second pair of perpendicularly disposed coils 60 and 62 are connected in series to coils 54 and 56, respectively, by means of wires contained in cables 64 and 6-6, respectively. A later detailed description of these coils will be given. A second rotor coil 68 is mounted within the last pair of perpendicularly disposed coils 60 and 62 and one end of the wire thereon is connected to each of the slip rings I0 which are aiiixed to the vertical shaft I2 upon which rotatable coil 68 is mounted. Coils 60, 62 and 68 form a second goniometer designated generally by I4 in Figs. 1 and 2. A pair of brushes I6 engage slip rings I0 and by means of wires in cable 16 .are connected to two of the brush-es designated generally by 80 which are carried by brush block 82. Each of the brushes 80 is connected to one of the pins 84 by means of one of the slip rings 86, and it will be seen that cable 88 contains two wires each of which connects with one of the pins 84. These two wires carry the current from slip rings I0 into radio receiver 90. A pair of earphones 92 is connected to the radio receiver by means of cable 94. This radio receiver is of the type customarily used in todays aircraft having the usual tuning means operable over the band of frequencies employed in aircraft navigation, as well as volume control means. Radio transmitter 40 likewise is capable of generating radio frequencies over this same range.

Referring still to Fig. 2, gear 96 is rigidly affixed upon the lower end of shaft I2 and a second gear 98 meshes with gear 96 and with pinion I00 which is mounted upon the lower end of the output shaft I02 of a Selsyn-type receiver I04. This receiver is connected by means of wires contained in cable I06 to a plurality of the brushes I03, each of the wires being connected to one of the brushes. Each of these brushes in turn contacts one of the slip rings H0 and each of these slip rings is connected to one of the pins I I2 at the top of the assembly. Cable II3 contains a plurality of wires each of which connects with one of the pins I I2 at one end and with the Selsyn-type transmitter I I4 at the other end. The input shaft N6 of this transmitter is rigidly affixed by means of coupling II8 to the upper end of shaft I20 which is the output shaft of differential designated generally by I22. The primary input of this differential is by means of gear I24 and the shaft I26 upon which it is rigidly affixed. Gear I24, it will be seen, meshes with gear I28 which is rigidly affixed upon the upper end of vertical shaft I30 upon the lower end of which is fixedly mounted antibacklash gears E33 which mesh with ring gear 22. It will be recalled that ring gear 22 is fixedly mounted in low-er bearing housing I8.

In Fig. 1, it will be seen that vertical shaft I30 enters a boxlike structure I32 which is referred to in the art as the heading gear box. The mechanism contained in this gear box is enclosed in dotted lines in Fig. 2. It will be seen that inside the heading gear box I32 and fixed upon vertical shaft I30 is another gear I34 which meshes with a smaller gear I36. This last-mentioned gear is fixed upon a second vertical shaft I38 which has rigidly mounted upon its upper end bevel gear I40 which meshes with a second bevel gear I42 affixed to a horizontal shaft I44. The right end of this last-mentioned shaft enters another boxlike structure I46 which represents the wind drift instrument which is described in detail in the copending application of Gnnne Lowkrantz and myself, Serial No. 406,056, filed August 8, 1941. It is to be noted that the recorder 31 is connected to the wind drift instrument I46 by means of electrical connections I48 and IE0 which are carried by a single cable I53. The wind drift instrument as explained in the mentioned copending application provides means for making the speed of the recorder 3'! responsive to the changes in the assumed ground speed of the trainer.

The secondary input of differential I22 is in the form of antibacklash gear I52 driven by worm I54 which is connect-ed by means of flexible cable I56 to pinion I58 engaging gear I60 which is driven by crank I62. Crank I62 is mounted upon shaft I64 upon which gear IE0 is rigidly affixed and upon the lower end of shaft I64 is pinion I66 which meshes with gear I66. A stub shaft centered upon gear I66 has mounted upon its upper end pinion I10 which drives gear I12 and which in turn rotates azimuth scale I'I4 by means of shaft I I6. Azimuth scale H4 is graduated from zero to 360, and a suitable reference mark (not shown) is fixed upon the inside of fuselage I0 in order that the position of azimuth scale I14 may be readily determined.

The functioning of my radio system is as follows: The output of the source 40 of modulated radio frequency carrier waves is fed to rotatable transmitting antenna 44. The radiations of transmitting antenna 44 induce a current in each of the pair of perpendicularly disposed coils 54 and 56 which surround coil 44. The coils 54 are in reality a single coil because they are formed of a continuous piece of wire, this single coil being split into two sections to allow the positioning of vertical shaft 46. By means of the two wires in :cable .64 the current flowing in coil .54 as :a re- 'sult of the voltage induced therein is carried to boil which is also a single coil divided into two sections. Therefore the two coil sections 54! are connected in series with the two coil sections .60 and the same current induced in coil .54 flows in coil .60.

Sections 56 likewise are a single coil as are sections '62, and the first two mentioned sections are in series with the last two by \drtue of the wires in cable 65. Therefore, the same current flows in both of these coils.

The currents flowing in sections 60 and 52 set up a field having a pattern dependent upon the currents induced therein. The current induced in sections 54 depends upon the position of rotatable transmitting coil 44 relative to sections '54, and therefore, the current induced in sections 60 depends upon the position of coil 44. The pattern set up about sections 62, it will be understood, in turn depends upon the position of coil 44. At the same time, the current .induced .in sections 56 and 62 and the'field pattern set up by section 62 will also depend upon the position of coil 44. The field pattern set up by sections 60 and 62 therefore depends upon the position of coil 44, and the current induced in rotatable coil 68 by the fields of sections 60 and 62 depends upon the position of coil 68 relative to these last mentionedsections. When coil 68, which acts as the directional .receiving antenna, bears the same relationship to its surrounding sections 68 and :62 that coil 44 bears to sections '54 and 56, the maximum current is .induced in the receiving antenna 68 and therefore the maximum signal is heard in earphones 92. If coil 68 is moved 90 degrees from this position of maximum interception, no current is induced in this coil, and therefore, no signal is heard in the earphones .92. This no signal position simulates the position of the receiving loop in a real plane relative to the path of the waves from a real transmitting station when no signal is picked up, which position, as stated previously, is referred to as the null position. If coil 68 is moved 90 degrees further, a second maximum signal position is realized, while at a further 90 degree position is another null position.

The current induced in coil 68 is led to slip rings =10, is picked up by brushes 76, carried by the wires in cable I8 to brushes 80, slip rings 86, pins 84, and by the wires in cable 88 to radio receiver 90, Receiver 90 amplifies, detects and further amplifies theaudio components of the signal generated by transmitter 40 so that these signals may be heard by earphones 92. For any signal to be received by earphones 92 receiver 90 must be tuned to the same carrier frequency generated by transmitter 40.

Also seen in Fig. 2, whenever the trainer rotates, shaft I 30 is rotated by gears I33 meshing with ring gear 22. Gear I28 is rotated, rotating gear I 26 which is the primary input of difierential I22. The output shaft I20 is rotated as is the input shaft IIB of Selsyn-type transmitter H4. Ihe rotation of the input shaft I I6 of this transmitter in either direction produces, by means of the wires in cable H3, pins II2, slips rings III], brushes I 08 and the wires within cable I06 a rotation of the output shaft I02 of theSelsyn-type receiver I04 through the same angle and in the desired direction. This system of remote actuation :is well known in the art. Pinion I00 is thereforerturned as isgear 98,.gear 96,shaft I2, slip rings 10 and the rotatable directional receiving antenna .coil 68.

It will be seen, therefore, that a rotation of the trainer fuselage Ill automatically rotates directional receiving antenna coil .68. The immediately aforedescribed system comprises such ratios that antenna 68 is rotated through the same angle as the trainer is turned. (It should be noticed that in the absence of this system no rotation of the coil 68 would occur as a result of the rotation of the trainer because this coil is positioned in one of the drawers of the desk '35.)

A reference to Fig, 2 also discloses that a rotation of loop control crank I62 rotates gear I61] and pinion I58, which, by means of flexible shafting I56 rotates worm I54,-the secondary drive I52 of differential I22, the output shaft I20 of this differential, and the input shaft I16 of Selsymtype transmitter I I4 resulting in a rotation of the output shaft I62 of the Selsyn-type receiver F04 through the same angle as input shaft IIG of transmitter I I4 is rotated. Simulated directional receiving antenna 68' is rotated by this rotation of output shaft I02.

From the foregoing, it will berealized that there are two movements which will cause a rotation of simulated directional receiving antenna =68, viz., a rotation of the trainer fuselage and a rotation of loop control crank I62.

The immediately aforedescribed system is synchronized with the trainer as follows: Transmitter 40 is set to generate a radio frequency carrier wave of any desired frequency and this Wave is modulated by any suitable audio frequency source, as explained in the copenclin-g application Serial Number 440,950. Radio re ceiver is tuned to the same frequency-as the carrier generated by source MI and the volume control of the receiver is set togive a low level signal. Azimuth control knob 48 which indicates the direction of the assumed geographical position of the trainer from the assumed ge0- graphical position of the radio station simulated by transmitter '40 is set so that it points to the zero on azimuth scale 50. The trainer is placed on an assumed east heading, and crank I6I is rotated, thereby rotating receivingantenna 68, until a null or no signal is heard in earphones 92. Inasmuch as azimuth control knob 48 and its associated scale 50 indicate the, assumed direction of the trainer from the assumed position of the radio station being simulated, it is clear that when this knob is set at zero, as has been done, the traineris assumed to be due north of the station. Furthermore, inasmuch as it is assumed that the trainer is flying due east .at a point directly north of the station, the relative bearing of the station with respect to the longitudinal axis of the trainer must be 90. Consequently, pinion I58 is disconnected from flexible shafting I56 and crank I62 lsrotated until azimuth scale I'M indicates a reading of 90. The flexible shafting I56 is then reconnected with pinion I 58. Then, directional receiving antenna 68 is loosened so that it may turn upon shaft .12, and antenna .68 is turned until no signal or .a null .is heard in earphones 92. The receiving antenna is then aflixed upon shaft 12 to turn therewith. The positionsof directional receiving antenna 68, heading of the trainer :IE), position of azimuth scale I14 and position of transmitter azimuth control knob A8 are then properly-synchronized.

It is .clear that if thereafter the trainer is erotate-d through a .given number of degrees, -'e. g.,

twenty-five, by means of ring gear 22, gear I33, shaft I30, gear I28, gear I24, differential I22 and shaft I the input shaft II6 of transmitter II 4 is rotated through a certain angle, its direction depending upon the direction of rotation of the trainer, the output shaft I02 of receiver I04 is rotated through the same angle as the input shaft II6 of transmitter H4 and directional receiving antenna 68 is rotated through an angle equal to the angle of rotation of the trainer. The null which wa received when the mechanism was synchronized as above will no longer be received by the navigator in the trainer and, therefore, he must rotate crank I62 to bring rotatable directional receiving coil 68 back to the null position. The new bearing to the assumed radio transmitting station with respect to the longitudinal axis of the aircraft will be indicated by azimuth scale I14.

It is clear, therefore, that a null once having been received, a rotation of the trainer will cause a disappearance of the null by rotating directional receiving antenna 68 just as in the case of a plane in actual flight where the null having once been obtained disappears by a turning of the plane. Furthermore, the student must by means of crank I62 change the position of directional antenna 68 to receive the null, and the new bearing to the station may be determined by a reference to azimuth scale I'I4. This practice exactly simulates the steps that the radio man in a real plane must perform to secure the bearing of a radio station by the null method.

Having synchronized the apparatus with the trainer on a due east heading at a point directly north of the transmitting station, let us assume that instead of the trainer changing its heading it proceeds eastward. It is clear that if a plane due north of a transmitting station and flying due east had its loop in the null position, eastward travel would cause a disappearance of the null because the loop would no longer be in a plane parallel to the path of the radiated waves. Consequently, with my aforedescribed apparatus, a the instructor views the travel of the recorder 31 eastwardly over map 36, the assumed direction of the trainer from the radio station no longer will be due north but will be east of north. The instructor therefore rotates azimuth knob 48 so that it indicates on scale 50 the assumed direction of the trainer from the assumed position of the transmitting station, as determined by the position of the recorder 31 upon map .36 relative to the assumed location of the radio station as shown upon the map. This rotation will rotate transmitting antenna 44 and the voltages induced in coil sections 54 and 56 and in sections 60 and 62 will be varied. Consequently, the field set up by sections 60 and 62 will be of a different pattern and directional receiving antenna 68 will no longer be positioned with respect to this different field pattern to intercept no signal. Therefore, the student in the trainer must rotate loop control crank I 62 to bring rotatable coil 68 into a position Where no signal is picked up by receiving antenna 68. The rotation of crank I62 simultaneously rotates azimuth scale I74 and when no signal is heard in earphones 92 receiving antenna 68 has been rotated through the same angle as transmitting antenna 44. The new bearing of the radio station with respect to the longitudinal axis of the trainer may be determined by the student by a reference to scale I'I-4.

It has been stated that when directional receiving antenna 68 bears the same relationship to its surrounding coil sections that transmitting antenna 44 bears to its surrounding coil sections, maximum current is induced in the receiving antenna 68 and, therefore, the maximum signal is heard in earphones 92. But if antenna 68 is moved 90 from this position of maximum signal interception no current is induced in this antenna and, therefore, no signal is heard in the earphones 92, It is clear, therefore, that for each position of transmitting antenna 44 there are two positions of receiving antenna 68 which will give no signal or a null in the earphones 92. These positions are 180 apart, and therefore, for each position of antenna 44 the student in the trainer will get a null position when azimuth scale I14 is in a certain position and when it is 180 from that position. The student in the trainer will ordinarily be able to tell which of the two positions 180 apart of azimuth scale I I4 indicates the correct assumed direction of the radio station with respect to the assumed direction of the longitudinal axis of the trainer because the general assumed position of the trainer relative to the radio station should be known to him. This elimination of the reciprocal of the true bearing of the assumed radio station to the trainer simulates the same practice which the navigator of a real plane must follow because the loop antenna of a real plane likewise has for any given station at any given place two null positions.

From the foregoing, it will be readily understood that my invention provides improved means for simulating the taking of radio bearings in a grounded aviation trainer. These means comprise in general means whereby the instructor may set up a field pattern depending upon the assumed direction of the trainer from the radio station, means whereby a rotation of the trainer automatically affects the strength of the signals intercepted by the directional antenna, and additional means which the student may use to bring a simulated directional receiving antenna into the null position.

Also seen in Fig. 2 is a unit I connected by means of cable I 82 to a unit I84 which is connected by means of Wires in cables I86 and I88 to the perpendicularly disposed goniometer I4, in the same manner that the perpendicularly disposed coil sections 54 and 56 are connected to sections 60 and 62. Unit I80 is similar in all respects to transmitter 40 and unit I84 contains a pair of perpendicularly disposed coil sections, a rotatable coil and azimuth indicating means identical with perpendicularly disposed coil sections 54 and 56, rotatable coil 44 and azimuth indicating means 48 and 50. The provision of these duplicate means make it possible to simulate two transmitting systems. The perpendicularly disposed coil sections 60 and 62 have the frequencies generated by both of the transmitting stations 40 and I80 flowing therein but no interference between the two transmitting stations occurs because the carrier frequencies used in actual practice are sufficiently different. The student in the trainer will, of course, hear the audio signals generated by only one of the transmitting stations because he can intercept signals only when his receiver 90 is tuned to the frequency of the transmitting station 40 or I80. The provision of duplicate transmitting systems makes it possible, by means of my invention, to simulate the common practice of determining a radio fix which is accomplished by determining the relative bearings from the longitudinal axis of the plane of two radio stations, the location of the plane being at the intersection of the bearings,

Inasmuch as the second transmitting system is identical with the first completely described system, it is deemed unnecessary to give a detailed description of its construction, synchronization and functioning. Directional receiving antenna 68 functions in relation to unit I84 exactly as described in relation to goniometer B.

The foregoing being but a preferred embodiment of my invention numerous details may be made in the construction thereof without departing from the substance of the invention.

I claim:

1. In a grounded navigation training system of the type including a fuselage rotatably mounted upon a stationary base and a flight simulating device remotely situated from and controlled by said fuselage and arranged to travel over a chart to indicate the assumed geographical position of the fuselage, means for simulating the operation of radio direction findin equipment carried by planes in actual flight, said means comprising, in combination, a signal source connected to a directional transmitting antenna unit, said directional transmitting antenna unit having a part movable to establish a directional field variable in accordance with the assumed bearing of said fuselage from a radio station as determined by the location of said flight simulating device upon said chart, a directional receiving antenna disposed in the field established by said transmitting antenna unit, signal receiving means in said fuselage connected to said directional receiving antenna, a Selsyn-type receiver located adjacent said directional receiving antenna and mechanically connected thereto for moving the same, a Selsyn-type transmitter electrically connected to said Selsyn-type receiver, means operated by the rotation of said fuselage relative to said stationary base connected to said Selsyn-type transmitter for actuating the same, means within said fuselage selectively operable by an operator and differentially combined with said means operated by the rotation of said fuselage for operating said Selsyn-type transmitter, and index means within said fuselage operable in response to an operation of said selectively operable means within said fuselage.

2. In a grounded navigation training system of the type including a fuselage rotatably mounted upon a stationary base and a flight simulating device remotely situated from and controlled by said fuselage and arranged to travel over a chart to indicate the assumed geographical position of the fuselage, means for simulating the operation of radio direction finding equipment carried by planes in actual flight, said means comprising, in combination, a signal source located outside said fuselage connected to a directional transmitting antenna unit located outside said fuselage, said directional transmitting antenna unit having a part movable to establish a directional field variable in accordance with the assumed bearing of said fuselage from a radio station as determined by the location of said flight simulating device upon said chart, a directional receiving antenna disposed in the field established by said transmittin antenna unit, signal receiving means in said fuselage connected to said directional receiving antenna, a Selsyn-type receiver located adjacent said directional receiving antenna and mechanically connected thereto for moving the same, a Selsyn-type transmitter located near said fuselage and electrically connected to said Selsyn-type receiver, means operated by the rotation of said fuselage relative to said stationary base and connected to said Selsyn-type transmitter for actuating the same, means within said fuselage selectively operable by an operator and difierentially combined with said means operated by the rotation of said fuselage for operating said. Selsyn-type transmitter, and index means within said fuselage operable in response to an operation of said selectively operable means within said fuselage.

KARL A. KAIL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,825,462 Link Sept. 29, 1931 2,099,857 Link Nov. 23, 1937 2,164,412 Koster July 4, 1939 2,312,962 De Florez' Mar. 2, 1943 2,321,799 Cone June 15, 1943 2,326,764 Crane Aug. 17, 1943 2,326,766 Delareuelle Aug. 17, 1943 2,332,523 Norden Oct. 26, 1943 2,346,693 Lyman Apr. 18, 1944 

